CuIn1-xGaxSe2 (CIGS) based thin film solar cells continue to show promise in the renewable energy market due to a steady gain in their solar energy conversion efficiencies in commercial scale devices. Cadmium sulfide is a thin film material used in conjunction with CIGS based thin film solar cells. An n-type cadmium sulfide layer is provided between a p-type absorber layer (as embodied as a CIGS film) and transparent conductive layer, and ensures efficient charge transport from the absorber to the electrical contact provided by the n-type transparent conductive oxide layer. The cadmium sulfide layer is commonly called a buffer or window layer when incorporated into a CIGS based thin film solar cell.
A cadmium sulfide layer can be typically formed by a chemical bath deposition (CBD) in a batch process. However, for vacuum deposited CIGS films, a chemical bath deposition process may not be a viable solution. It is practically impossible to integrate a chemical bath deposition process into a roll to roll deposition process, or a continuous deposition process, that deposits thin film solar cell materials.
Other methods of depositing a cadmium sulfide layer using physical vapor deposition are possible. One such method is magnetron sputtering under vacuum of a stoichiometric cadmium sulfide target to a surface of an absorber substrate (i.e., a CIGS film) to form a thin cadmium sulfide layer.